settingenviron: Set MAKEFLAGS for parallelism in ~lfs/.bashrc

1 files changed, 49 insertions, 0 deletions

diff --git a/chapter04/settingenviron.xml b/chapter04/settingenviron.xml
index b255a4b45..2d8d6045f 100644
--- a/chapter04/settingenviron.xml
+++ b/chapter04/settingenviron.xml
@@ -195,6 +195,55 @@ EOF</userinput></screen>
      completed LFS system.</para>
   </important>
 
+  <para>
+    For many modern systems with multiple processors (or cores) the
+    compilation time for a package can be reduced by performing a "parallel
+    make" by telling the make program how many processors are available via
+    a command line option or an environment variable.  For instance, an Intel
+    Core i9-13900K processor has 8 P (performance) cores and
+    16 E (efficiency) cores, and a P core can simultaneously run two threads
+    so each P core are modeled as two logical cores by the Linux kernel.
+    As the result there are 32 logical cores in total.  One obvious way to
+    use all these logical cores is allowing <command>make</command> to spawn
+    up to 32 build jobs.  This can be done by passing the
+    <parameter>-j32</parameter> option to <command>make</command>:
+  </para>
+
+  <screen role='nodump'><userinput>make -j32</userinput></screen>
+
+  <para>
+    Or set the <envar>MAKEFLAGS</envar> environment variable and its
+    content will be automatically used by <command>make</command> as
+    command line options:
+  </para>
+
+  <screen role='nodump'><userinput>export MAKEFLAGS=-j32</userinput></screen>
+
+  <important>
+    <para>
+      Never pass a <parameter>-j</parameter> option without a number to
+      <command>make</command> or set such an option in
+      <envar>MAKEFLAGS</envar>.  Doing so will allow <command>make</command>
+      to spawn infinite build jobs and cause system stability issue.
+    </para>
+  </important>
+
+  <para>
+    To use all logical cores available for building packages in
+    <xref linkend='chapter-cross-tools'/> and
+    <xref linkend='chapter-temporary-tools'/>, set <envar>MAKEFLAGS</envar>
+    now in <filename>.bashrc</filename>:
+  </para>
+
+<screen><userinput>cat &gt;&gt; ~/.bashrc &lt;&lt; "EOF"
+<literal>export MAKEFLAGS=-j<replaceable>$(nproc)</replaceable></literal>
+EOF</userinput></screen>
+
+  <para>
+    Replace <replaceable>$(nproc)</replaceable> with the number of logical
+    cores you want to use if you don't want to use all the logical cores.
+  </para>
+
   <para>Finally, to ensure the environment is fully prepared for building the
   temporary tools, force the <command>bash</command> shell to read
   the new user profile:</para>